BOUILLON, AGAR AND MILK. 



237 



While the filter is still hot, and the pump active, the 

 well sedimented agar (p. 236) is slowly poured on the cen- 

 ter of the filter. The liquid passes through as rapidly as it 

 strikes the surface. The impurities are brought last upon 

 the filter. If the filtrate is not perfectly clear, it can be 

 passed through the filter a second or a third time. The 

 operation of filtration requires but a few minutes. The 

 resulting filtrate, when 

 filled into tubes and 

 sterilized, is usually 

 wholly free from a de- 

 posit, and is perfectly 

 transparent. At most, 

 a few floccules will 

 separate during the 

 subsequent steriliza- 

 tion. 



In order to facili- 

 tate the filtration 

 through paper many 

 workers prefer to 

 make a 1 or 1^ per 

 cent, solution of agar. 

 While it is true that 

 such solutions filter 

 more readily, yet this 



advantage is more than offset by the softer consistency 

 of the agar. The two per cent, agar prepared as above is 

 hard, and though it is not filtered through paper, it is,, 

 nevertheless, perfectly clear. 



The above method of making agar would seem to be 

 long and tedious, but in reality, it is no more difficult than 

 the preparation of gelatin. While the pump is very useful, 

 in the above filtration, it is by no means necessary. 



In the method as described, the agar is not added to- 

 the albuminous meat extract, but to the ready-made bouil- 



FIG. 35. Apparatus for filtering agar (F. G. N.). 



